1. Field of the Invention
The invention is directed to an improved fuel injection system for an internal combustion engine.
2. Description of the Prior Art
One fuel injection system of the type with which this invention is concerned is known from European Patent Disclosure EP 0 987 431 A2. This fuel injection system has one high-pressure fuel pump, and one fuel injection valve communicating with it, for each cylinder of the engine. The high-pressure fuel pump has a pump piston, which is driven in a reciprocating motion by the engine and which defines a pump work chamber. The fuel injection valve has a pressure chamber communicating with the pump work chamber and also has an injection valve member, by which at least one injection opening is controlled, and which is movable, being acted upon by the pressure prevailing in the pressure chamber, in the opening direction counter to a closing force in order to open the at least one injection opening. A first electrically actuated control valve is provided, by which a communication of the pump work chamber with a relief chamber is controlled. By means of a control piston, a control pressure chamber is defined, and the control piston, acted upon by the pressure prevailing in the control pressure chamber, acts on the injection valve member in the closing direction. The control pressure chamber has a communication, controlled by a second electrically actuated control valve, with a relief chamber. For a fuel injection, the first control valve is closed and the second control valve is opened, so that high pressure cannot build up in the control pressure chamber, and the fuel injection valve can open. With the second control valve open, however, fuel flows out of the pump work chamber via the control pressure chamber, so that the fuel quantity available for the injection, from the fuel quantity pumped by the pump piston, and the pressure available for the injection is reduced as well.
The fuel injection system of the invention has the advantage over the prior art that because of the communication of the control pressure chamber with the work chamber defined by the second pump piston, when the second control valve is open for the fuel injection and the fuel injection valve is thus also open, no fuel flows out via the pump work chamber, and thus all the fuel pumped by the first pump piston, and the pressure generated by the first pump piston in the pump work chamber, are available, undiminished, for the fuel injection.
Other advantageous features and refinements of the fuel injection system of the invention are disclosed. For example, one embodiment makes a space-saving disposition of the second pump piston possible. Another embodiment in a simple way makes slaving of the second pump piston after the initial stroke of the first pump piston possible.